Save an image of a web page (including Flash content) to a file. Web page screenshots may be captured interactively or from the command line. Options allow you to control the output format (PNG or JPEG), image file name, scaling, and much more.
Here is more about the Pearl Crescent Page Saver from the developers:
Page Saver lets you capture images of web pages, including Flash content. A web page screenshot can be saved in PNG or JPEG format. Using Page Saver, you can capture an entire page or just the visible portion. To allow you to control the image capture process, a wide variety of options are provided including a file name pattern and an image scale setting (e.g., save at 50% of original size).
Want to learn more? Check out Pearl Cresent Page Saver on the Firefox Add-ons website.